Recently, attention has been directed to a direct injection spark ignition type internal combustion engine in which fuel is directly injected into a combustion chamber of the engine. In this type of engine, the combustion mode is switchingly controlled corresponding to an engine driving condition, i.e., the combustion mode is switchingly controlled between stoichiometric combustion (sioichiometric homogeneous combustion) and lean combustion (stratified lean combustion or homogeneous lean combustion) (see Japanese Unexamined Patent Publication No. 59-37236).
However, in a direct injection spark ignition type internal combustion engine, fuel is directly injected into a combustion chamber of the engine, so that the torque sensitivity of a fuel system is increased (i.e., torque does turn out to vary by a large amount even with a slight change of fuel injection amount). Thus, if the amount of fuel injection is instantaneously increased such as due to trouble of fuel system part, there may be caused an abrupt change of behavior of the vehicle, resulting in deterioration of driveability.
The present invention has been carried out in view of the conventional problems as described above, and it is therefore an object of the present invention to avoid deterioration of driveability such as due to trouble of fuel system part.